A fuel cell is an electrochemical device in which the energy from a chemical reaction is converted directly to electricity. The basic concept was described as far back as 1840 and relies on an anode and cathode separated by an electrolyte. During operation a continuous flow of fuel, commonly hydrogen, is fed to the anode while simultaneously a continuous flow of oxidant, commonly air, is fed to the cathode. The fuel is oxidized at the anode in a catalyzed reaction with the release of electrons. These electrons are conducted to the cathode, through wires external to the cell (to the load), where the oxidant is reduced and the electrons recombined again through the agency of the catalysts. The external flow of electrons from anode to cathode constitutes electrical current which can be made to do useful work.
The type of fuel cell which is in the most advanced state of development and which is near commercial power plant use employs on concentrated phosphoric acid as an electrolyte and operates at about 325.degree. F.-425.degree. F.
The efficiency at which the cell operates is determined by several parameters, including the catalyst activity. The catalyst is necessary since it permits the fuel cell to operate at lower temperature thereby reducing thermal losses which would otherwise reduce efficiency. Over the years there have been many attempts to find inexpensive highly active catalysts. However, the choice of catalytic materials is severely limited since any catalyst which is effective for the purpose must not only have a high activity for the reactions involved, but must also be capable of withstanding the high temperature working environment while being exposed to a strong acid.
Initially catalysts were made of platinum or other noble metals as these materials were catalytically active and were able to withstand the corrosive environment of the cell. While these elements were first used in solid form, later techniques were developed to disperse these metals over the surface of electrically conductive supports (e.g. carbon black) to increase the catalyst surface area which in turn increases the number of reaction sites leading to improved cell efficiency. It was also discovered that certain noble metal alloys, particularly platinum, displayed increased catalytic activity permitting further increases in fuel cell efficiencies. Some of these alloys are platinum-chromium (commonly assigned U.S. Pat. No. 4,316,944) and platinum-vanadium (commonly assigned U.S. Pat. No. 4,202,934). It was also discovered that a ternary catalyst contained platinum, cobalt and chromium was even more effective and this is described in commonly assigned U.S. Pat. No. 4,447,506. These three patents are incorporated by reference. These improved catalysts made possible increased fuel cell efficiency which makes possible the greater utilization of fuel cell technology. However, the search continues for stable catalysts with increased activities for the electrochemical reduction of oxygen.
European Pat. No. 0149293 describes a catalyst containing platinum and gallium. This catalyst is described as being useful in fuel cell applications and is alleged to provide improvements in catalytic activity and in long-term stability.